Clarification of the physiological function of the bio functional substances, such as a protein and a nucleic acid has been an important task. In addition thereto, control and design of the physical chemical properties are indispensable for realization of a bioreactor, a biosensor, a DNA chip, and for the near further, a bio element, or the like. Therefore, development of the analysis methods for the physical chemical properties of the bio functional substances and analysis reagents for the measurement is expected.
A bio functional substance has the activity in an organism, and the organism has water as a medium. Therefore, clarification of the physical chemical properties should be carried out in an aqueous solution. As an analysis method effective for examining the structure of a bio functional substance and the interaction with the substrate molecules in water, the Raman spectroscopy as a kind of the vibration spectroscopy method has been provided.
However, since the signal intensity obtained by the ordinary Raman spectroscopy is extremely low and the sensitivity is poor, a specimen concentration of several % or more has been required. Therefore, in the case of a bio functional substance, a specimen condensing operation is necessary and indispensable so that problems are involved in the cost, and the risk of losing or denaturation of the specimen during the operation.
In contrast, even in the case of the Raman spectroscopy, if a specimen interacts with metal fine particles, the surface enhancing effect of amplifying the signal intensity is known (“Surface enhanced Raman Scattering”, ed. By R. K. Chang and T. E. Furtak, (Plenum Publishing; N.Y., 1982)). The enhancing sensitivity is said to be in general from 10,000 times to 1,000,000 times.
The surface enhancing effect appears dramatically in the case the above-mentioned metal fine particles are used in an aggregated state. A measuring method utilizing the surface enhancing effect is important also as a study method for the biotechnology (K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, and M. S. Feld, Biomedical Applications of Lasers, 77 (7), 915-924 (1999); Surface-enhanced Raman scattering: A new tool for biomedical spectroscopy).
According to a recent experiment using aggregation of precious metal fine particles, the surface enhancing effect reaching as much as 100,000,000,000,000 times capable of one molecule detection has been confirmed (K. Kneipp, H. Kneipp, R. Manoharan, E. Hanlon, I. Itzkan, R. R. Dasari, and M. S. Feld, Applied Spectroscopy, 52 (12), 1493-1497 (1998); Extremely large enhancement factors in surface-enhanced Raman scattering for molecules on colloidal gold clusters). Such metal fine particles are referred to as the substrate of the surface enhancing effect. Semiconductors such as a gallium and a gallium arsenide can also be the substrate.
As embodiments at the time of using metal fine particles as the substrate for the surface enhancing effect, a colloid of metal fine particles, a film with metal fine particles deposited on the surface in an island-like form, a glass matrix with metal fine particles dispersed in the inside by a sol gel method, a polymer matrix with metal fine particles dispersed in the inside, or the like has been reported so far. Moreover, the present inventors have also disclosed in the official gazette of the Japanese Patent Application Laid Open (JP-A) No. 11-61209 a technique for obtaining a stable dispersion of the precious metal fine particles by producing precious metal fine particles by the reducing reaction in a dispersion with plate-like fine particles of a swellable layered silicate, or the like dispersed.
Among the substrates, a colloid of nano precious metal fine particles in an aqueous solution is regarded as most convenience in the practical use. As the reason therefor, advantages such as 1) capability of synthesizing fine particles in a liquid phase method, and facilitation of handling, 2) adoptability to a continuous flow analysis system, 3) capability of controlling the particle size and the shape, 4) capability of easily defining the surface area, and 5) capability of changing the morphology for the theoretical analysis, have been pointed out (M. Kerker, D. S. Wang, H. Chew. O. Siiman, and L. A. Bumm, “Surface Enhanced Raman Scattering”, ed. by R. K. Chang and T. E. Furtak, (Plenum Publishing, N.Y., 1982), pp. 109-128; Enhanced Raman scattering by molecules adsorbed at the surface of colloidal particles).
In any case, in order to use metal fine particles as the substrate for the surface enhancing effect, the dispersion state should be maintained stably. Conventionally, as the method for controlling the dispersion state, since the metal fine particles are lyophobic fine particles, 1) addition of a stabilizing agent in a liquid phase, 2) deposition onto a solid phase (including coating), 3) containment into a matrix of the above-mentioned glass, polymer, or the like, 4) coexistence of a swellable layered silicate with metal fine particles as mentioned in the above-mentioned official gazette of the Japanese Patent Application Laid Open (JP-A) No. 11-61209, or the like have been proposed.
Among these controlling methods, as a stabilizing agent to be used in a liquid phase, a surfactant such as a sodium dodecyl sulfate, a polyvinyl alcohol, a polyvinyl pyridine, a polyethylene glycol, an N-vinyl pyrrolidone, a bovine serum albumin, a γ-globulin, and a protective colloid such as a gelatin are known. Moreover, the “method for preventing colloid aggregation” of the Japanese Patent Application Laid Open (JP-A) No. 09-070527 discloses the stabilizing effect of a buffer agent such as a tris(hydroxymethyl)amino methane, or the like.
Moreover, as the deposit onto a solid phase, a method of depositing fine particles on a glass plate and stopping aggregation at a stage of a certain degree is frequently used. According thereto, it is possible to deposit the nano fine particles synthesized by the liquid phase method on the glass plate, thereby producing aggregations with different sizes and morphologies.
However, even if a stabilizing agent is used, it has been extremely difficult to maintain the aggregation state in the liquid without precipitation while maintaining the function of the fine particles in the dispersion phase of the lyophobic fine particles with a liquid used as the dispersion medium such as a colloid of precious metal fine particles in an aqueous solution. As a result, the reproductivity and the stability of a production method for a substrate of the surface enhancing effect dependent on the aggregation state of the lyophobic fine particles have been poor, and the performance is still insufficient.
Moreover, since the conventional stabilizing agent prevents aggregation by restraining approach of the fine particles with each other by adhering on the surface of the fine particles, the surface activity, which is an important function of the metal fine particles, is lost. Even in the case the metal fine particles are deposited on the solid phase, the dispersion and the deviation of the aggregation size distribution are large so that the reproductivity of the production method is poor, and furthermore, it is instable, and thus the stability can be maintained for about several days at most even if they are coated with an organic monomolecular layer such as a thiol. According to the containment in a matrix, loss of the surface activity of the metal fine particles by the matrix, and deterioration of the substance moving rate in the matrix are generated so that a substrate with the excellent surface enhancing effect cannot be obtained. The technique disclosed in the official gazette of the Japanese Patent Application Laid Open (JP-A) No. 11-61209 produces metal fine particles in a dispersion with plate-like fine particles dispersed so that a long time is required for the production of the metal fine particles, resulting in rise of the cost, and furthermore, since an acetone dicarboxylic acid, which can easily be decomposed, is used as the reducing agent, it is inconvenient in terms of handling.
That is, a substrate with the surface enhancing effect, being stable for a long time, capable of providing a quick response, to be produced with a good productivity while maintaining a high surface activity of the lyophobic fine particles, has not been known so far.
Therefore, an object of the present invention is to provide an analysis method of keeping lyophobic fine particles existing in a group as aggregation to be a dispersed phase, and using the obtained dispersion complex as the practical substrate of the surface enhancing effect.